Guidelines - Drilling

Terminology

All tool list information is treated as 'unfinished' unless instructed otherwise. This information is placed in 'read.me' files.

Hand Assembly

The .042" is a very versatile size for proto typing. It's finished size (.039")is a bit too sloppy for machine assembly ( IC's and resistors ), but it's great for hand assembly.

In many cases you could use .028, .035 and .042 for most of the board's IC and related "glue" hardware. The larger diameters will come into play for interconnects, transformers and mounting hardware etc.

Always Measure With Calipers

It is best that you never "guess" when it comes to the size of the required hole. Instead use calipers to measure the devices you intend to use.

Using Calipers:

• squeeze the device into the calipers.
• carefully rotate the device's lead in the caliper so that the largest surface feature is measured (especially important for flat or square pins).
• add approximately .010" for plating.

Note: Some component leads are very delicate. Be careful you don't twist them out of shape. It may be necessary to relax the caliper's grip when rotating the lead.

Example: a dual row ribbon cable header that uses a .100" space from pin center to pin center and is square posted. The actual measurement (cross corner) will be in the .032" to .036" range. Adding .005"~.010" would suggest that you may want to drill it at .039"~.046". Ideally you also want to maintain a minimum .010" annulus on the pad after it's drilled (improves solderability) , this would then indicate that you should use a .061"~.066" pad.

Plating Reductions

Over sizing of a pin by .010" is a generous measurement and will include the plating factor. Hole sizes in a plated through hole board reduce by .003"~.005" from the drilled size.

In the previous example (using the ribbon cable header) we established a required minimum finished diameter of .036 using calipers. The minimum unfinished diameter this device should be drilled with is .038". After plating you may be required to apply some force to insert the header. Changing the unfinished diameter to .042", eases the insertion problem, allows for some minor misalignment of the pins (slightly bent), and in the case of proto typing your board with our facility, uses a free drill diameter.

Calculations

A device that has a symmetrical square post can use the following calculation:

For example the following calculation will be required to provide the absolute minimum diameter of a "finished hole" for a .025" square post: